Many electronic devices, including watches, remotes, toys, and other devices, leverage the benefits delivered by lithium coin cell batteries. These primary power sources are thin, portable, and affordable, in addition to providing reasonably high voltage and capacity. As such, the use and further adoption of primary (i.e., non-rechargeable) lithium coin cell batteries is expected to continue to grow for the foreseeable future.
Lithium coin cell batteries come in a variety of sizes, although they are generally small, circular discs possessing standardized dimensions and nominal voltages. Exemplary sizes, with reference to their International Electrotechnical Commission designations include CR2016, CR2025, and CR2032, which are generally 20 mm in height and 1.6 mm, 2.5 mm, and 3.2 mm (respectively speaking) in diameter, and all possess a lithium-manganese dioxide chemistry producing a nominal voltage of 3.2 volts. Many coin cell manufacturers prefer to impart reflective and/or high quality metals, plating, or coatings on the outer casings of such batteries in order to improve their appearance and/or performance.
Unfortunately, the size and appearance of these batteries have led to individuals ingesting the batteries, particularly infants and small children. Numerous cases have been documented in which these batteries have been accidentally ingested, and in some instances the battery becomes lodged in the digestive tract (and especially the esophagus with respect to children), choking, severe injuries, and even deaths have been reported.
In most cases of battery ingestion and especially those in which young child is involved, it may not be possible to determine the existence of a problem until well after the onset of serious health problems. Moreover, information about when and what type of battery was ingested cannot be easily established, which makes it extremely difficult to verify the nature of the problem and devise appropriate medical interventions in response to it.
The battery and device manufacturing industries have recently begun developing measures to reduce the possibility of accidental swallowing of foreign objects, such as improved packaging, warning labels, and screw-fastened battery compartments on devices. However, numerous incidents result from an unsupervised child ingesting a loose battery that was been left unattended after removal from its original package or from a device.
The present inventors have found that ingested batteries lodged in the esophagus lead to an electrochemical interaction between the battery and human tissue. Keeping in mind that water in saliva may undergo an electrolysis reaction producing hydrogen gas and hydroxide ions, the ingested, lodged battery can produce electrical current causing the in situ electrolysis of saliva and localized alkaline burns/perforations of the esophagus.
Past disclosures did not fully appreciate the reaction mechanisms and resulting dangers caused by ingested coin cells remaining lodged in the digestive tract. For example, U.S. Pat. No. 5,069,989 describes an alkaline battery cell design intended to avoid corrosion of the positive electrode by acidic gastric juices found in the stomach. Specifically, a corrosion-resistant container consisting of a stainless steel having more than 23% chrome is proposed, with the preferred embodiment having a nickel coating layer on the positive electrode can intended to prevent the release of hexachrome ions from the stainless steel.
International Patent Publication No. WO 2013/106821 describes the use of specific grades of stainless steel and/or metal coatings or claddings for use on the exterior of coin cells. This publication theorizes that the use of exterior materials with sufficiently high overpotentials for the reactions inherent to electrolysis and/or the concomitant metallic oxidation of the casing should reduce or eliminate the localized, in situ formation of hydroxide by ingested and lodged coin cells. However, subsequent experimentation suggests that even the slightest imperfection in these materials severely reduces or entirely eliminates the efficacy of this proposed solution. Accordingly, while based on theoretically sound principles, this publication has proven impractical owing to constraints in how cell casings must currently be manufactured.
Other prior publications indicate more passive solutions. For example, United States Patent Publication No. 2014/170074 describes compositions and methods for deterring and/or visually identifying oral contact/ingestion of coin cells. In particular, emetics, aversives, and colorants are applied to the exterior of the cell via a carrier. These additives, respectively speaking, are intended to induce vomiting, create unpalatable tastes, and provide an indication that the cell has come into contact with saliva. However, in the event the coin cell is swallowed using these or other similar approaches (e.g., see United States Patent Publication No. 2014/0030570; International Patent Publication No. WO 2012/164429: Japanese Patent Publication Nos. JP S5929353, JP S5951455, JP H04312762, and JP S59211955; and Great Britain Patent Publication Nos. GB 2254806 and GB 2265807), immediate medical intervention is still required, as these solutions do nothing to mitigate the problematic electrolysis reaction byproducts.
Still other approaches contemplate altering the conditions under which the coin cell can be discharged in the first instance. Fundamentally, these solutions are premised on redesigning battery compartments to exert unique forces on the battery casing. As one example, United States Patent Publication No. 2015/0020436 discloses a conductive, pressure-sensitive coating that ensures that the battery only delivers current when sufficient compression is delivered. Other physically activated, pressure-sensitive switches integrated within the battery housing have also been contemplated.
Separately, 1.5 volt alkaline button cells are known to leak in certain environmental conditions (e.g., high humidity). Known solutions to this problem rely upon retaining the structural integrity of button cells (and other batteries containing alkaline solutions) by preventing or mitigating the leakage/unwanted release of harmful or toxic materials already contained within the cell. U.S. Pat. No. 4,258,108 discloses a moisture-protected, sealed ring including anhydrous, weak inorganic acids that bind alkaline electrolyte that might escape from the cell. U.S. Pat. No. 4,107,403 describes an edge portion coating provided to electrochemical cells including a thermoplastic resin containing hydrogen bonding functional groups. In each instance, these solutions contemplate the release of existing materials from the battery under expected or ambient conditions and, therefore, are not analogous to the unique complications presented by ingestion of higher voltage coin cells.
Given these proposals, it is desirable to provide for an electrochemical cell construction that can mitigate or delay damage to human tissue from inadvertent ingestion by responding to the conditions provoked by that ingestion.